Pulsed oscillator



Aug. 19, 1947. W HAUSZ ET AL PULSED OSCILLATOR Filed Octl. 2'7,` 1944Fig.

P41/E VL 73465 Patented Aug. 19, 1947 PULSED OSCILLATOR Walter Hausz andAlfonso Alvira, Schenectady, N. Y., assignors to General ElectricCompany, a corporation of New York Application October 27, 1944, SerialNo. 560,541

(Cl. Z50-36) Claims.

Our invention relates to electron discharge oscillators and, moreparticularly, to pulsed input circuits for such oscillators arranged tocontrol the operation of the oscillator so that oscillations aregenerated in short, recurrent bursts or pulses.

It is a general object of our invention to provide new and improvedvpulsing means for an electron discharge oscillator.

It is a further object of our invention to provide a new and improvedtriggered input circuit for electron discharge oscillators.

It is still another object of our invention to provide an oscillatorgrid pulsing circuit characterized particularly by ease in starting andsimplicity in keying operation.

Another object of our invention is the provision of new and noveltriggering means for controlling the repetition rate of pulses ofoscillations in a self-blocking oscillator.

Briefly, our invention comprises an electron discharge oscillator of theself-blocking type having an input circuit including means for normallybiasing the grid beyond cutoi and means for recurrently supplying to thegrid short pulses or surges of positive potential to initiateoscillations.

Our invention itself will be more fully understood and its objects andadvantages further appreciated by referring now to the followingdetailed specication taken in conjunction with the accompanying drawingin which Fig. 1 is a schematic circuit diagram of a pulsed oscillatorembodying our invention, and Figs. 2 and 3 are graphical representationsof certain voltage relations characteristic of an oscillator embodyingour invention.

Referring now to the drawing, and particularly to Fig. 1, we have shownan electron discharge oscillator comprising an electron discharge deviceI having an anode 2, a cathode 3, and a control electrode 4. By way ofillustration only, we have shown the discharge device I connected as atuned plate-tuned grid oscillator. It will of course be understood bythose skilled in the art that our invention is not limited in its scopeto application to an oscillator of this particular type, but may beapplied equally well to oscillators of other well known types. Thetuned-plate-tuned-grid oscillator shown comprises a tuned plate circuit5 comprising an inductance 6 and a Variable capacitor 1 connected inparallel circuit relation between the anode 2 and the positive terminalof a source of unidirectional potential such as a rectier 8 connected toa suitable source of alternating current supply (not shown) through aswitch 9 and a voltage control device such as a variable voltagetransformer I0. A by-pass-condenser I I connected across the rectiiier 8reduces to a negligible value the impedance oiered by the rectier tooscillatory currents. The negative terminal of the rectifier v8 isconnected to the cathode 3. A resistor 3a connected across the switch 9maintains constant output voltage on the rectilier 8 when the load isremoved, thereby to facilitate easy starting.

The input or control electrode circuit of the discharge device I isconnected between the control electrode 4 and the cathode 3, andincludes a tuned circuit I2 comprising an inductance I3 and a variablecapacitor I4. The circuit I2 is tuned to a frequency differing slightlyfrom the frequency of the generated oscillations in such a sense thatthe tuned circuit I2 has the effect of an inductance in the inputcircuit. The input circuit also includes means interposed between thecontrol electrode 4 and the cathode 3 for normally biasing the controlelectrode suiciently negative to maintain the discharge device I cutoff. Such biasing means comprises a resistor I5 and a condenser I6connected in parallel circuit relation and across a source ofunidirectional potential. The unidirectional biasing potential sourcecomprises a transformer having a secondary winding I'I connected acrossthe condenser I6 through a diode rectifier I8 and a primary winding I9connected to the output terminals of the variable voltage transformerI0, or other suitable source of alternating current supply. Connectionof both the plate supply rectifier 8 and the bias supply rectifier I8 tothe same variable voltage source of alternating current, as to thetransformer I0, ensures that the bias potential from rectifier I8 willvary directly with the plate or anode voltage. Since the tube cut-offvoltage varies with plate voltage the interconnection of plate and biasvoltage sources maintains the negative biasing potential across thecondenser I6 substantially proportional to cut-off voltage.

The oscillator input circuit includes also a delay circuit 2u connectedin series with the circuit I2 and the resistor I5 and comprising aresistor 2I and a condenser 22 connected in parallel circuit relation.The condenser 22 has a capacitance sufiicient automatically to blockoscillations in the discharge device I a predetermined time afterinitiation of such oscillations. charges the condenser 22 during theinterval between pulses. In order to vary the duration of pulses ofoscillations in the discharge device I,

The resistor 2| disswitch 28 to a. suitable source of variable voltagealternating current supply, such as a. variable voltage transformer 29.The secondary winding 30 of the transformer 26 is connected in seriescircuit relation in the input circuit of the oscillator. Connected inparallel circuit relation with the transformer secondary winding 38, weprovide also a condenser 3I and a quenching diode 32,. The diode 32 isconnected to short-Circuit the Winding 30 for negative voltages acrossthe Winding, so' that such negative voltages are suppressed anddo notappear upon the oscillator grid 4.

The'control elements of the transformers I9 and129 are interconnected sothat their output voltages' vary in intensity in like manner. By thisinterconnection operation of the oscillator over a wide range of anodevoltage is rendered possible, since the intensity of grid triggeringpulsesis made proportional to the negative bias potential across thecondenser I6. For example, as anode voltage increases so that the tubecutoff voltage is greater, the bias potential across condenser IGincreases proportionately and maintains the grid 4 farther belowcut-off. To overcome this the'transformer 29 increases the intensity ofthe triggering pulses applied to the input circuit through thetransformer 26.

`As will appear more fully hereinafter, the transformer. 29 may beconnected to an alternating current source of any frequency below apredetermined maximum frequency determined by the discharge time of thecondenser 22. Preferably the switches 9 and 28 are also interconnected,so that when the switch 28 is opened to remove triggering pulses fromthe input circuit and remove the load on the rectifier 8 the resistance9a is inserted in the rectier input circuit to maintain the rectifieroutput voltage normal.

In the drawing we have shown an indicating instrument 33 and a resistor34 connected in series in the input circuit of the oscillator I andshunted by a capacitor 35. It will of course be understood by thoseskilled in the art that the instrument 33 is included for indicatingpurposes only but may, if desired, be omitted.

A by-pass condenser 36 is connected to shunt all elements of the inputcircuit except the tuned circuitY I2 for currents at oscillatorfrequency.

In view of the foregoing description of the circuit arrangement of ournew and improved pulsing oscillator, the operation of the oscillatorwill now be understood from the following description.

I In the absence of output voltage from the peaking transformer 28, thesubstantially constant charge maintained on the condenser I6 through therectifier I8 is suicient to maintain the control electrode 4 belowcut-off, so that the discharge device I is nonconductive. Thethree-legged peaking transformer 26 having an air gap in the unwoundVcenter leg is of a construction well known to those skilled in the art.When a sine waveofvoltage is impressed upon the primary winding 2'I ofsuch a transformer, the transformer leg upon which the secondary winding30 is wound exhibits a flat-'topped flux characteristic by reason 4 ofsaturation of this leg. Accordingly, therefore, pulses of voltage areinduced in the secondary winding only during the relatively shortperiods of reversal of flux through the secondary winding. These pulsesare alternately positive and negative, each cycle of the alternatingprimary voltage supplying one positive and one negative pulse. Thenegative pulses are quenched in the discharge device 32 which isconnected to short-circuit the transformer winding for voltages of suchpolarity. The positive pulses, however, appear at the terminals of thewinding 30 and raise the voltage of the control electrode 4 suncientlyto initiate oscillations in the discharge device I.

At Fig. 2, we have shown a curve of grid bias voltage plotted againsttime wherein the foregoing relations appear. On this curve, the brokenline 31 indicates the cut-off voltage of the control electrode 4. At thetime T=0, the control electrode is biased below cut-off to a negativevoltage 38 by the action of the rectifier I8 and condenser I6. Thepositive voltage pulses impressed on the input circuit by the peakingtransformer' 26 are indicated in broken lines at 39'and 39a. Thesepulses are shown on an exaggerated time scale to illustrate more clearlythe operation of the circuit. As indicated at Fig. 2,

the net grid voltageshown in the unbroken line increases from 38 to avalue above cut-off upon the appearance of the pulse 39. At some pointslightly above cut-off, as at a time T1, the discharge device I becomesconductive. This is indicated at Fig. 3, which shows the variation ofanode voltage with time.

After initiation of oscillations in the discharge device I, theoscillations build up rapidly by reason of the interelectrode capacitivecoupling between the anode 2 and the control electrode 4. As the anodepotential oscillates due to energy storage in the tuned circuit 5, thegrid potential also oscillates in opposite phase relation by reason ofthe capacitive anode-to-grid coupling through the interelectrodecapacitance and the effectively inductive grid-to-cathode couplingthrough the tuned circuit I2. The oscillations of grid potential takeplace around the instantaneous grid biaspotential shown by the solidcurve at Fig. 2. As the grid oscillations build up, they so'on reach apoint where the instantaneous net grid'potential exceeds the cathodepotential once per cycle ofthe oscillations. Whenever the grid 4 ispositive, it draws grid current, thereby to charge the condensersV 22,I6, 3I and 35, in such a direction as to bias the grid negative withrespect to the cathode. The capacitance of the condenser 22, or thecombined capacitance of the condensers 22 and 24 if the switch 25 isclosed, is such that the grid is driven rapidly negative by gridcurrent', as indicated by the line 40 at Fig. 2. The rate at which thegrid bias voltage increases in a negative sense due to grid current isof vcourse affected by the condensers I6, 3I and 35, but thesecondensers are so chosen that their effect is small compared to theeffect of the con-l densers 22 and 24. Since the grid oscillations takeplace about the instantaneous grid bias potential shown in fullflines atFig. 2, it is evident that the grid is soon biasedsonegative that thegrid oscillations. fail to attain even the cut-off potential. VAt thispoint, as at a time T2, the discharge device I is automatically blockedby the actionof its' own input circuit, Aand oscillations cease.

When the oscillations in the dischargedevice I cease at the time T2, thegrid 4 is left with a large negative potential. It will be noted that atsuch time the positive pulse 39 has not yet passed, so that the netinstantaneous grid voltage following the time T2 will be the resultantof the latter portion of the pulse 3S, the negative bias voltage 38across the resistor I5, and the voltage of the condenser 22 as itdischarges through the resistor 2l. As the negative charge on thecondenser 22 decays and the pulse 39 passes, the resultant instantaneouspotential of the control electrode 4 follows a curve such as indicatedat fila, il of Fig. 2. The portion I of the grid voltage curve is theresultant of discharge of the condenser 22 and the last portion of thepulse 39. The portion il of the grid voltage curve shows the effect ofcondenser discharge alone after passage of the lpulse 39. The condenser22 is almost completely discharged and the grid voltage restored to thenormal bias valve 33 prior to the occurrence of the next positive pulse39a from the transformer 28.

The function of the capacitors l5, 3l and 35 will now be clear. Thesecapacitors are connected across the resistor l5, the transformer winding30 and the instrument 33, respectively, in order to conduct the largegrid current which flows during blocking operation, as in the timeinterval 'I1- T2 at Fig. 2. The grid current would otherwise cause verylarge voltages across the shunted elements and preclude pulse typeoscillation. It may now be noted also that the connection of thecapacitor 3l across the winding 353 forms a resonant circuit which tendsto oscillate at its natural frequency after each triggering pulse acrossthe transformer winding 3B. The quenching diode 32 serves to suppresssuch oscillations, as well as to suppress negative induced pulses ashereinbefore described.

It will now be noted that the duration of the output pulses from theoscillator tube I is determined by the time taken for grid current inthe tube l to drive the control electrode suiiiciently negative to blockthe oscillations. This time is indicated at Fig. 2 as the time interval'T1-T2, and is determined by the magnitude of grid current andcapacitance of the condenser 22, taken in connection with the totalcapacitance of the other condensers in the input circuit. Moreover, thetime between output pulses, that is, the frequency or repetition rate ofthe pulses, is determined by the frequency of the alternating currentsource connected to the peaking transformer 25 through the transformer29. The maximum permissible repetition rate is limited, however, by therate of discharge of the condenser 22 through the resistor 2|, since thetriggering pulses, 39, 39a from the transformer 26 must be spaced apartin time by at least the time taken for the condenser 22 to dischargesufficiently to allow the triggering pulse to take effect. Thisdischarge time is controlled by the resistor 2 l. It is for the purposeof Controlling the duration and maximum frequency of the pulses that weprovide the additional R. C. circuit 23, 24 which may, if desired, beconnected in parallel circuit relation with the circuit 2i, 22 by meansof the switch 25.

While we have described only a preferred embodiment of our invention byway of illustration, many modifications will occur to those skilled inthe art and we therefore wish to have it understood that we intend inthe appended claims to cover all such modifications as fall within thetrue spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination, a vself-pulsing Voscillator including an electrondischarge device having an anode, a cathode and a control electrode,input and output circuits connected to said device and coupled tosupport oscillations, said input circuit being connected between saidcathode and control electrode, means for supplying to said controlelectrode a negative biasing potential sufficient normally to maintainsaid discharge device nonconductive, means comprising a source ofalternate positive and negative potential pulses connected in series insaid input circuit for impressing pulses on said control electrode, eachof said positive pulses having suicient intensity to overcome saidbiasing potential and initiate said oscillations, and a second electrondischarge device connected across said source to suppress said negativepulses therefrom, whereby only said positive pulses are effective insaid input circuit.

2. In combination, a self-pulsing oscillator including an electrondischarge device having an anode, a cathode and a control electrode',linput and output circuits connect-ed to said device and coupled tosupport oscillations, said input circuit being connected between saidcontrol electrode and cathode, meansV for supplying to said controlelectrode a negative biasing potential suflicient normally to maintainsaid discharge device non-conductive, means comprising a peakingtransformer having a secondary winding connected in said input circuitfor periodically impressing alternate positive and negative voltagepeaks thereon, and a second electron discharge device connected inparallel circuit relation with said secondary winding to suppressnegative voltage peaks across said winding, each of said periodicpositive pulses from said transformer having suiicient amplitude toovercome said biasing potential and initiate oscillations in said rstdischarge device.

3. In combination, a self-blocking oscillator including an electrondischarge device having an anode, a cathode, and a control electrode,input and output circuits connected to said device and coupled tosupport oscillations, said input circuit being connected between saidcontrol electrode and cathode, means for supplying to said input circuita negative bias potential sufcient normally to maintain said dischargedevice nonconductive, a peaking transformer having a secondary windingconnected in said input circuit and a primary winding connected to asource of alternating current thereby periodically to induce in saidsecondary winding alternate positive and negative potential pulses,means comprising a condenser connected in parallel circuit with saidsecondary winding for by-passing grid current of said oscillator, and asecond electron discharge device connected in parallel circuit relationwith said secondary winding to suppress negative pulses across saidsecondary Winding and to quench oscillations across said condenserfollowing said positive pulses, whereby said positive pulsesperiodically initiate oscillations in said first discharge device.

4. In combination, a self-pulsing oscillator comprising an electrondischarge device having an anode, a cathode, and a control electrode,input and output circuits connected to said discharge device andregeneratively coupled to support oscillations, said input circuit beingconnected between said control electrode and cathode and including meansfor effecting grid current blocking of said oscillator, means forbiasing said control electrode suiciently negative normally to preventsaid oscillations, means including an inductive element connected inseries circuit relation in said input circuit for supplying recurrentpulses of positive potential to said control electrode, a condenserconnected in parallel circuit relation with said inductive element toconduct said grid current, and a second electron discharge deviceconnected in parallel circuit relation with said inductive element tosuppress oscillations in said inductive element following said positivepulses.

5. In combination, a self-pulsing oscillator comprising an electrondischarge device having an anode, a cathode, and a control electrode,input and output circuits connected to said discharge device andregeneratively coupled tosupport oscillations, said contro] electrodecircuit being connected between said control electrode and cathode andincluding means for eifecting grid current blocking of said oscillator,means for biasing said control electrode suiciently negative normally toprevent said oscillations, a saturable core transformer having asecondary winding connected in series circuit relation in said inputcircuit and a primary winding connected to a source of alternatingcurrent, a quenching diode connected across said secondary winding tosuppress negative pulses across said secondary winding, and a condenserconnected in parallel circuit relation with said secondary winding toconduct said grid current, said diode suppressing oscillations tendingto arise across said transformer and condenser following positive pulsesfrom said transformer.

WALTER HAUSZ.

ALFONSO ALWRA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

